Institute of Histology and General Embryology, University of Siena, Italy.

A fibrillar elastic apparatus around the wall of human lymph capillaries is demonstrated by means of histochemical and ultrastructural techniques. This apparatus consists of three interlinked components listed here in order of increasing distance from the capillary wall: 1) oxytalan fibres connected to the abluminal surface of the endothelial cells, known also as "anchoring filaments" and consisting of bundles of microfibrils; 2) elaunin fibres consisting of microfibrils and a small amount of elastin; and 3) typical elastic fibres consisting of microfibrils and abundant elastin. The microfibrillar constituent has similar ultrastructural features in the three components of the elastic apparatus. Microfibrils have a diameter of 12-14 nm, an electron-transparent core and a wall with 3-5 electron-dense subunits and oblique cross striations with a period of 15-17 nm. Microfibrils are the common element of the three components of the elastic apparatus and they link them to one another and to the elastic network of the perivascular connective tissue. An elastic apparatus was not found around blood capillaries and it can thus provide a histological marker to identify lymph capillaries. The possible role of the lymphatic elastic apparatus in the physiological activity of the lymphatic absorbing network is discussed and it is proposed that its disconnection from the elastic network of the tissue may promote pathological conditions such as lymphoedema or diseases related to impaired immune responses.

PMID: 2337247 [PubMed - indexed for MEDLINE

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Hi vnb11

Welcome to our family!!

Excellent topic. Have to tell you I have been scouring trying to find follow up reports, studies anything... so far haven't been successful.

For those who want to go direct to the article you posted the links is:

It is interesting that though these related articles seem to show great promise, there is nothing written after 1996.

Very much appreciate you posting this and if I find anything new, I will certainly put it on here.

There is a vascular clinic in Italy, associated with the University of Milan and Parma. They have placed us on their lymphedema page as a link for information. I wonder if we wrote to them, they could provide additional information, since the original work was done in Italy.

In previous studies "anchoring filaments" of human lymphatic capillaries have been shown to consist of microfibrils having histochemical and ultrastructural characteristics similar to elastin-associated microfibrils. When not associated with an elastin component, these microfibrils are referred to as "oxytalan microfibrils." In this study, alpha-glycol-containing carbohydrates and glycoconjugated sulfate groups, originating from sulphydryls and/or disulfide bridges, have been detected in anchoring filament microfibrils of human lymphatic capillaries by Thiery reaction (PA-TCH-SP) and "Hight Iron Diamine" cytochemical method (HID), respectively. Both of these chemical groups belong to the putative glycoprotein of which the microfibrils are constituted. Similar molecular characteristics have been demonstrated in elastic fiber microfibrils and oxytalan microfibrils of connective tissue. These findings suggest a close molecular similarity among these different types of microfibrils. Thus, whatever their individual location or denomination (anchoring filaments, oxytalan fibers, or elastin-associated microfibrils), these microfibrils form an uniform population of fibrous elements. These findings further support a structural (and functional) continuity between the lymphatic capillary wall and the elastic network of adjacent connective tissues previously described and termed "Fibrillar Elastic Apparatus" (FEA). Of interest, endothelial cells also selectively react positively to the PA-TCH-SP and HID methods.

Initial lymph vessels of the skin and elastic fibres form an integral morphofunctional structure.

Gerli R, Alessandrini C.

Institute of Histology and General Embryology, University of Siena, Italy.

Little has been published on the histochemical and cytochemical properties of anchoring filaments of the initial lymph vessels. Previous research suggests that the microfibrils of the anchoring filaments have ultrastructural, histochemical and cytochemical characteristics similar to those of the microfibrils associated with the elastic fibres. With the aim of further investigating the histological identity of anchoring filaments, we performed an immunohistochemical study in human skin lymphatics, using the antibody HB8, specific for elastic fibre microfibrils. There is now a body of evidence suggesting a new concept in the framework of the lymphatic system. It unifies the initial lymph vessels, the anchoring filaments and the satellite elastic fibres in a single and integral entity.

An immunological correlation between the anchoring filaments of initial lymph vessels and the neighboring elastic fibers: a unified morphofunctional concept.

Solito R, Alessandrini C, Fruschelli M, Pucci AM, Gerli R.

Institute of Histology and General Embryology, University of Siena, Italy.

Little has been published on the histochemical and cytochemical properties of anchoring filaments of initial lymph vessels. Previous research suggests that the microfibrils of the anchoring filaments have ultrastructural, histochemical and cytochemical characteristics similar to those of the microfibrils associated with elastic fibers. With the aim of further investigating the histological identity of anchoring filaments, we performed an immunohistochemical study with human skin lymphatics, using antibody HB8, specific for elastic fiber microfibrils. The findings suggested strong molecular similarities between elastic fibers and the fibrils of anchoring filaments of the initial lymph vessels. A comparison of these fibrils showed both constitutional homogeneity and structural continuity from the abluminal surface of the initial lymph vessel to the perivascular elastic fibers and to the adjacent elastic network of connective tissue. In conjunction with previous findings, we propose a unified hypothesis that the elastic fiber system composed of anchoring filaments, perilymphatic sheath and adjacent connective tissue acts by alternating stretching and relaxation to propel lymph towards lymph collectors and draining lymph nodes.

Structural biology of the fibres of the collagenous and elastic systems.

Montes GS.

Laboratory for Cell Biology, University of Sao Paulo School of Medicine, Brazil.

The different types of fibres of the collagenous and elastic systems can be demonstrated specifically in tissue sections by comparing the typical ultrastructural picture of each of the fibre types with studies using selective staining techniques for light microscopy. A practical modus operandi, which includes the recommended staining procedures and interpretation of the results, is presented. Micrographs and tables are provided to summarize the differential procedures. Reticulin fibres display a distinct argyrophilia when studied by means of silver impregnation techniques, and show up as a thin meshwork of weakly birefringent, greenish fibres when examined with the aid of the Picrosirius-polarization method. In addition, electron-microscopic studies showed that reticulin fibres are composed of a small number of thin collagen fibrils, contrasting with the very many thicker fibrils that could be localized ultrastructurally to the sites where non-argyrophilic, coarse collagen fibres had been characterized by the histochemical methods used. The three different fibre types of the elastic system belong to a continuous series: oxytalan-elaunin-elastic (all of the fibre types comprising collections of microfibrils with, in the given sequence, increasing amounts of elastin). The three distinct types of elastic system fibres have different staining characteristics and ultrastructural patterns. Ultrastructurally, a characteristic elastic fibre consists of two morphologically different components: a centrally located solid cylinder of amorphous and homogeneous elastin surrounded by tubular microfibrils. An oxytalan fibre is composed of a bundle of microfibrils, identical to the elastic fibre microfibrils, without amorphous material. In elaunin fibres, dispersed amorphous material (elastin) is intermingled among the microfibrils.

The elastic system of normal human skin was studied by light and electron microscopy. By light microscopy three different types of fibers were observed: oxytalan, elaunin, and elastic. The most superficial ones (oxytalan fibers) are very thin and directed perpendicularly to the dermoepidermal junction. They start from a plexus with the tinctorial characteristics of elaunin fibers which is connected with the thicker elastic fibers of the reticular dermis. At the electron microscopic level the oxytalan fibers are formed by bundles of tubular microfibrils 10 to 12 nm in diameter. In the deepest layers of the dermis an amorphous material is seen in the core of these bundles. In the elaunin fibers the amorphous material is sparse, while in the elastic fibers it is abundant and compact.

Association of elastin with oxytalan fibers of the dermis and with extracellular microfibrils of cultured skin fibroblasts.

Schwartz E, Fleischmajer R.

The formation of a mature elastic fiber is thought to proceed by the deposition of elastin on pre-existing microfibrils (10-12 nm in diameter). Immunohistochemical evidence has suggested that in developing tissues such as aorta and ligamentum nuchae, small amounts of elastin are associated with microfibrils but are not detected at the light microscopic and ultrastructural levels. Dermal tissue contains a complex elastic fiber system consisting of three types of fibers--oxytalan, elaunin, and elastic--which are believed to differ in their relative contents of microfibrils and elastin. According to ultrastructural analysis, oxytalan fibers contain only microfibrils, elaunin fibers contain small quantities of amorphous elastin, and elastic fibers are predominantly elastin. Using indirect immunofluorescence techniques, we demonstrate in this study that nonamorphous elastin is associated with the oxytalan fibers. Frozen sections of normal skin were incubated with antibodies directed against human aortic alpha elastin and against microfibrillar proteins isolated from cultured calf aortic smooth muscle cells. The antibodies to the microfibrillar proteins and elastin reacted strongly with the oxytalan fibers of the upper dermis. Oxytalan fibers therefore are composed of both microfibrils and small amounts of elastin. Elastin was demonstrated extracellularly in human skin fibroblasts in vitro by indirect immunofluorescence. The extracellular association of nonamorphous elastin and microfibrils on similar fibrils was visualized by immunoelectron microscopy. Treatment of these cultures with sodium dodecyl sulfate/mercaptoethanol (SDS/ME) solubilized tropoelastin and other proteins that reacted with the antibodies to the microfibrillar proteins. It was concluded that the association of the microfibrils with nonamorphous elastin in intact dermis and cultured human skin fibroblasts may represent the initial step in elastogenesis.

Endothelial cell connecting filaments anchor endothelial cells to the subjacent elastic lamina in the developing aortic intima of the mouse.

Davis EC.

Department of Anatomy, McGill University, Montreal, Quebec, Canada.

The ultrastructural association of endothelial cells with the subjacent elastic lamina was investigated in the developing mouse aorta by electron microscopy. In the 5-day postnatal aorta, extensive filament bundles extend along the subendothelial matrix connecting the endothelial cells to the underlying elastic lamina. The connecting filaments form lateral associations with the abluminal surface of the endothelial cells in regions of membrane occupied by membrane-associated dense plaques. On the intracellular face of each plaque, the termini of stress fibers penetrate and anchor to the cell membrane in alignment with the extracellular connecting filaments. Both the stress fibers and the connecting filaments are oriented parallel to the longitudinal axis of the vessel. High magnification electron micrographs of individual endothelial cell connecting filaments reveal features similar to those of elastin-associated microfibrils. Each connecting filament consists of a 9-10 nm linear core with an electron-lucent center and peripheral spike-like projections. From the filaments, small thread-like extensions span laterally, linking the filaments into a loose bundle and anchoring them to the endothelial cell membrane and the surface of the elastic lamina. The filaments also appear heavily coated with electron-dense material; often with some degree of periodicity along the filament length. During development, the number of endothelial cell connecting filaments decreases as the elastic lamina expands and the subendothelial matrix is reduced. In the aortic intima of mature mice, the elastic lamina is closely apposed to the abluminal surface of the endothelial cell and no connecting filaments are seen.(ABSTRACT TRUNCATED AT 250 WORDS)

Institute of Histology and General Embryology, University of Siena, Italy.

In contrast to their absence near dermal blood capillaries, elastic fibers are commonly seen adjacent to dermal lymphatic capillaries under light microscopy. Based on morphometric analysis, the elastic fiber network that surrounds these skin lymphatic capillaries is predominantly oriented longitudinally to the lymphatic vessel wall. Quantitative analysis reveals that the density of these pericapillary elastic fibers are almost twice that of the intercapillary elastic fibers but only about one-half as thick. These data suggest that dermal lymph capillaries are surrounded by a specific elastic network of functional significance, morphologically distinct from that seen in the intercapillary dermis. Because lymphatic capillaries are often difficult to identify especially when collapsed, this elastic network may facilitate the positive identification of dermal lymphatic capillaries by light microscopy and thereby help differentiate them from blood capillaries. The possible role of this lymphatic elastic network in the absorptive activity of the dermal lymphatic system is also discussed.

Using the tannic acid-glutaraldehyde fixation it was possible to clearly visualize, with reproducible results, the elastic fiber amorphous material because of its density. The microfibrillar component was also evidenced with a good performance. With this technique the ultrastructural patterns of the oxytalan and elaunin fibers were also demonstrated. The oxytalan fibers appeared as a bundle of microfibrils similar to elastic microfibrils without amorphous material. The elaunin fibers presented a dispersed amorphous material intermingled among the microfibrils. It was suggested by ultrastructural evidences that oxytalan and elaunin fibers may represent interruption in successive phases in the development of the elastic fibers.

The elastic fiber system in the human tracheal and bronchial mucosa was studied by light and electron microscopy. Elastic fibers, elaunin fibers, and oxytalan fibers were discerned. These fibers were identified by means of their staining characteristics (elastica stains, methods for disulfide-groups) and on account of their fine structural morphology. Elastic fibers consist of elastin and few "elastic-fiber microfibrils". The relative amount of elastin (compared to the amount of elastic-fiber microfibrils) is large in elastic fibers but small in elaunin fibers. Oxytalan fibers - by contrast - are pure bundles of microfibrils. In the light microscope a well-defined elastic lamina separates the lamina propria and the submucosa of the normal mucous membrane. The elastic lamina is formed by coarse strands of longitudinally running elastic fibers. A delicate network of elastica-positive fibers is attached to the basement membrane of the epithelial layer (subepithelial elastic layer). A few of these elastica-positive fibers branch out, traverse the region of the thickened basement membrane, and insert into the basal lamina of the epithelium. A loose network of elastica-positive fibers is present both in the lamina propria and in the submucosa. Plates of cartilage, glandular epithelium, and bundles of smooth muscle cells are enveloped by delicate elastica-positive fibers. Electron microscopy shows the lamina elastica to be predominantly composed of elastic fibers, whilst elaunin fibers form the subepithelial elastic layer. Fibers penetrating the thickened basement membrane of the epithelium are identified as oxytalan fibers. All three types of fibers are present throughout the lamina propria and in the submucosa.(ABSTRACT TRUNCATED AT 250 WORDS)

The microfibrils of anchoring filaments, a typical ultrastructural feature of initial lymphatic vessels, consist mainly of fibrillin and are similar to the microfibrils of elastic fibers. As we previously demonstrated, they radiate from focal adhesions of lymphatic endothelium to the perivascular elastic network. Although present in large blood vessels, fibrillin microfibrils have never been detected in blood capillaries. Here we report immunohistochemical evidence that cultured bovine aortic and lymphatic endothelial cells express fibrillin microfibrils. These microfibrils form an irregular web in lymphatic endothelial cells, whereas in blood vessel endothelial cells they are arranged in a honeycomb pattern. Cultured lymphatic and blood vessel endothelial cells also produce focal adhesion molecules: focal adhesion kinase, vinculin, talin, and cytoskeletal beta-actin. Our data suggest that anchoring filaments of initial lymphatic vessels in vivo may be produced by endothelium. Through their connection with focal adhesions, they may form a mechanical anchorage for the thin wall of initial lymphatic vessels and a transduction device for mechanical signals from the extracellular matrix into biochemical signals in endothelial cells. The complex anchoring filaments-focal adhesions may control the permeability of lymphatic endothelium and finely adjust lymph formation to the physiological conditions of the extracellular matrix. The different deposition of fibrillin microfibrils in blood vessel endothelial cells may be related to the necessity of withstanding shear forces. Thus, in our opinion, differences in fibrillin deposition imply a different role of fibrillin in blood vessel and lymphatic endothelium.